Power Source for Fire Pumps

[jwilson3]

I'm designing for 3-100HP electric fire pumps. Per NFPA 409 two of the pumps are to be adequate for the system demand with the 3rd pump as a standby. It's my interpretation that the transformer would be sized for 125% of the full load of two of the pumps, not three.(NEC 695.5(A)) The pumps are controlled by pressure. It takes two pumps to maintain the required pressure. I guess it's conceivable that a leak in the system could cause enough pressure drop during a fire so that the 3rd pump would come on, in which case I can see the need to include all pumps in the sizing.

A similar question arises with the Overcurrent Protection (NEC 695.5(B), which is to be sized to carry the locked rotor current of the "fire pump motor(s)". It's not likely, but it's not impossible for all three motors to be in locked rotor condition, which would lead me to include all three motors in the selection of rating.

I would appreciate comments.

 

[dpc]

Unless there are positive mechanical or electrical interlocks that prohibit all three pumps from running at once, then I would size service and OC protection for all three pumps running at the same time.

That probably also mean the ability to handle simultaneous locked rotor current of all three pumps indefinitely without tripping.

You could always make one engine-driven instead of electric.

 

[SooCS]

For offshore and marine industries, each of the firewater pumps is to have its own independent power supply. In your case failure of power supply all the three pumps will be out of service. This is not recommended and should not be acceptable.

As dpc suggested, you should have at least one engine-driven; probably two. If one pump is engine-driven, the other two electric pumps should be powered by both a emergency and the main power sources.

Best of luck.

 

[jwilson3]

Actually, there are two power sources; one is a backup source witrh auto-transfer in case of an outage on the normal source.